This invention relates to brush seal elements.
In many circumstances where it is desired to form a seal between a high pressure region and a low pressure region in a fluid part extending between two generally coaxial elements, in which one is moving, usually rotationally, with respect to the other it is known to form a seal using a pack of bristles associated with a backing plate, which extends substantially across the gap between the elements to limit the pressure induced reflection of the bristles. Often the backing plate itself is insufficient to overcome the problems arising from bristle deflection and proposals were developed in the mid 1990s to enable local area of higher pressure to be induced between the bristles and the backing plate so as to reduce the pressure drop across the bristle pack and hence the tendency of the bristles to deflect. Such proposals are well described in U.S. Pat. No. 6,173,962. Here it will be seen that the bristles are essentially spaced from a backing plate, which is, at some portion, cranked, or otherwise formed so that it can engage against the lower edge of the bristles.
Whilst technically these approaches work quite well, they can be expensive to manufacture because of the specialised machinery needed to form shaped backing plates; because a range of shaped backing plates need to be produced for different sized seals and different pressure environments and because where fluid supplied to the cavity is passed through the bristles, but it can be expensive and more complicated to form an appropriate bristle array, which provides good sealing at the ends of the bristles, but allows flow into the cavity.
From one aspect the invention consists in a brush seal element for sealing a region of high pressure from a region of low pressure, the element including an array of bristles and a backing member on the intended low pressure side of the seal the layer extending across a face of the backing member characterised in that the face is planar; the array is non-linear, when no pressure is applied, so that at least one portion of the array is spaced from the face to create a cavity there between and in that there is a fluid path for feeding pressurised fluid to the cavity to enable the pressure drop across the array to be reduced.
Various embodiments of this arrangement can be achieved. For example the non-linearity may extend substantially over the length of the array, so, for example, the layer may essentially be curved and additionally or alternatively the array may be held relative to the backing plates such that they diverge from the face when no pressure is applied.
In other embodiments the non-linearity may be localised along the length of the array and the non-linearity may be substantially triangular, square, rectangular or semi-circular in cross-section. Conveniently there may be a plurality of such non-linearities along the length of the array and there may be a variety of cross-sections.
It will be appreciated that creating cavities by forming different non-linearities into the bristle array is substantially cheaper than having to form ranges of backing plates and indeed this approach introduces substantial design freedom whereby, particularly where the brush elements are mounted side be side to form a seal, the performance of the seal can be adjusted along the length of the seal by forming different non-linearities in respective seal elements. A further significant advantage of this approach is that the formation of non-linearities increases the local porosity of the bristle array so that, in use, high pressure fluid can readily enter the cavity defined between the bristles and the plate and this is achieved without any loss of bristle density at the sealing edge of the element.
In some configurations, the cavity may not be closed, when no pressure is applied, because the pressure drop can be utilised to cause the bristle array to engage with the backing plate to define a boundary of the cavity.
As has been mentioned above the path for fluid may at least be in part through the bristle array and is most preferably located at or adjacent the non-linearity. Additionally or alternatively the path for pressurised fluid may at least in part be defined by a by-pass.
From a further aspect the invention consists in a brush seal element including bristles that are non-linear when the seal is not pressurised.
The invention also includes a seal assembly including a plurality of side-by-side elements as defined above.
Such an assembly may include seal elements having linear bristles to define end seals for a run of non-linear bristle seals.
Although the invention has been defined above, it is to be understood it includes any inventive combination of the features set out above or in the following description.